Studies were undertaken to demonstrate the ability of Factor B, an analog of vitamin B12, to bind to intrinsic factor. It was shown that this analog, which in pure form does not bind to intrinsic factor, will bind in significant quantities in the presence of small doses of vitamin B12. Maximum binding occurs at ratios of true vitamin B12 to analog of about 15 to 1. Similarly, uptake of analog rat midgut rings was shown to be uninfluenced by the presence of intrinsic factor, but in the presence of intrinsic factor in excess plus small quantities of true vitamin B12, absorption of analog was shown to occur. Studies are presently being conducted to determine whether the analog leaves the intestinal mucosal cell as does true vitamin B12 or whether the analog upon entry into the epithelial cell remains trapped and is subsequently shed with the epithelial cell. Such a mechanism would explain inability of the epithelial cell to take up vitamin B12 in the presence of large concentrations of analogs.